"President Obama has treated torture as an unfortunate policy choice rather than a crime.

"His decision to end abusive interrogation practices will remain easily reversible unless the legal prohibition against torture is clearly re-established."

In its 107-page report, HRW claims there is substantial information warranting criminal investigations of Mr Bush and his senior officials for ordering practises such as waterboarding, the use of secret CIA prisons and the transfer of detainees to countries where they were tortured.

Mr Bush has said he followed the advice of his legal advisers, who told him, for example, that the use of waterboarding on several Guantanamo inmates was legal.

The failure to investigate officials undermines US efforts to press for accountability for human rights violations abroad in countries like Libya and Sri Lanka, the group argues.